• Do you plot non-historical characters ahead of time? Or create them on the fly?
Since what we write is alternative history, I like to keep my historical characters reasonably true to their actual selves. If nothing else, it helps give the reader something (someone?) to hold onto. If we were really writing alternative history there might not be any familiar name at all, and I think that can hurt suspension of disbelief. Even if your main characters are your own invention, a famous name or two passing in the background helps make it feel real.
• Do you use a character sheet?
No. If I don't know who the characters are, they tell me - and sometimes they tell me off and go their own way, or change as we go.
If I don't know who my people are - the major characters and not the minors - then I had better not write until I do.
• Do you introduce character traits slowly, or all at once (less is more vs. info dump)?
I like to give characters a 'tell' or fit them into a category - old man, new guy, etc. Then I let them play against type if they want. Nothing helps make a character human like inconsistency.
• Do your characters drive the story?
Yes. off the cliff, usually. I am not good at writing characters - I try, but it is not my strong suit. But all too often, they decide they don't like the script (or me) and off they go.
• Or does the story drive the character?
Sometimes the story necessitates certain characters - you can't have Shakespeare's Hamlet if you put Sherlock Holmes in the title role, or vice versa.
Some stories just have to have certain people in them or they are not that story.
• Does the AAR length influence the amount of narrative detail you go into (i.e. AARs that last a few years vs 350+)?
Length. Ah, God. I completely lost control of Here There Be Dragons and the experience was horrifying. I tend to want to write short fiction but seem completely unable to do so. Length? I could write a thousand pages on a minor character debating his breakfast. The problem is stopping.
• How much research do you undertake when writing a historical personage, if any?
A fair bit - but, honestly, this is alternative history, so having them react in a way that seems true to the audience is better than lifting a response from a biography. And having a historical personage ring a bit false to their actual character can be useful, too.
• Do you plan or script the events ahead of crafting your AAR, or write it 'on the fly'?
Both. I generally know the kind of story I want to tell and I work out a few scenes that I know have to be in the story no matter how hard I have to work to get there.
I do pick up a lot from game events, and I always try to play ahead so that I don't write myself into a corner.
I have changed my mind about the ending, but I think I have to get that settled at least by the mid-point if I'm going to arrive on-target.
• Have any of your characters taken on a life of their own and forced unforeseen changes to the narrative?
Constantly. I used to resent it but got to where I realized they know what they're about better than I do - I mean, why have an invisible friend if you don't let him speak?
I have sometimes forced a character to do what I want, and I have always regretted it - that makes for bad writing.
• Do you serialize your posts? (i.e. end with a cliffhanger?)
I have done - gotta keep those addicts comin' back for another hit, after all. Not all that often, but I have sometimes done so.
• Do you prefer First Person (I, me, my), Second Person (you, your), Third Person (he/she, his/her) or Third Person Omniscient (same as TP but with full knowledge of events)
That entirely depends on what I'm writing. I think - for me - it is a question of immediacy. First person is very immediate - we are at one with the POV character and we experience what he or she does, in real time. It goes down the scale from there, with a cool Third Person Omniscient more suited for history-book passages.
. Seriously though, in a comedic sense, I'd like to think The SolAARium is not just for literary or elite purposes. It's function is to cover all aspects of writing and AARs. I think it's great you tackled the comedic aspects of the subject. Your answers and insight just expands its purpose. And those are wonderful answers. Comedic AARs have been around since the very early days. The works of @Peter Ebbesen, MrT, prufrock451, and @Duke of Wellington come to mind, as well as my Portugal or Bust: The Director's Cut - Rated 'R', a mini-series that takes a not so subtle shot at the movie and TV world. 
